Numerous studies have been conducted by combining RISs with many research fields. Assisting a relay system with an RIS [1]}, RIS-based index modulation[2]}, RIS-enabled reflection modulation [3]}, implementation of non-orthogonal multiple access (NOMA) by using RISs [4]}, [5]}, and channel modeling in the presence of an RIS [6]}, [7]}, [8]} can be given as examples. These studies have achieved a great success with the help of RISs by avoiding or abiding some of the negative effects of them, such as the double pathloss problem [9]}, [10]}, and lossy reflection through reflecting elements. For this reason, passive RISs only perform efficiently when they are positioned close to terminals and cannot go beyond being a supportive technology for the communication system. To overcome these unfavourable properties, some studies has been conducted by combining active elements with RISs. In [11]}, a single receive RF chain that includes a low-noise amplifier (LNA) was used to enable baseband reception, which in turn, was exploited for channel estimation at the RIS side. Similarly, channel estimation using a hybrid RIS architecture in [12]} has been done by deploying small numbers of receive RF chains at the RIS side. Another RIS-based channel sensing approach was studied in [13]} by coupling some amount of incident signal with a modified RIS architecture including some receive RF chains. Furthermore, [14]} analyzes dynamic metasurface antennas (DMAs) from an analog and digital signal processing perspective with much less number RF chains than the number of metamaterials. In [15]}, a reflection-type amplifier has been proposed to be used by all of the reflecting elements of an RIS, and the proposed amplifying RIS element was designed, fabricated, and used in an experiment. Another active reflecting element design has been proposed in [16]} such that the magnitude of the reflection coefficient of the reflecting elements is greater than unity. Connection of only a few elements of an RIS with RF chains and power amplifiers (PAs) has been investigated in [17]} as a hybrid relay-reflecting intelligent surface.
